1. Field of the Invention
The present invention relates to a copy machine, laser printer, facsimile device, or other image forming apparatus, and to a process cartridge thereof.
2. Description of the Related Art
The type of image forming apparatus that employs an electrophotographic process has conventionally had a charging device for charging the surface of a photoreceptor as an image carrier. A charging system that uses adjacent discharge is one example of a charging system used in the charging device. This is a system for charging the surface of a photoreceptor by adjacent discharge in which a charging member is brought into contact with, or brought near but not into contact with, the photoreceptor surface. Since increased resolution, miniaturization, and other features have been increasingly desired in recent years, increased resolution and small size have become objects in the charging device. A charging device with an adjacent discharge that uses a charging member in contact with or in proximity to a photoreceptor is effective for achieving these objects because a large-scale charging device is not required.
However, it has been learned that the photoreceptor surface is degraded due to the electrical discharge being concentrated in the vicinity of the photoreceptor surface in a charging system that uses adjacent discharge. Degradation of the photoreceptor surface by adjacent discharge differs from mechanical scraping in that it occurs even when there is no member in contact with the photoreceptor. As will be described hereinafter with reference to the drawings, degradation of the photoreceptor surface by adjacent discharge can be identified by the scraping or thinning of the film on the photoreceptor surface.
Enhancing frictional resistance by coating the surface of the photoreceptor with amorphous silicone carbide or enhancing frictional resistance by dispersing alumina or another inorganic substance into the charge transport layer (CTL) of the photoreceptor surface have been proposed in Japanese Unexamined Patent Application Publication No. 2002-207308, 2002-229227, and other publications, for example, in order to prevent the thickness of the film on the photoreceptor surface from being reduced. Although durability against mechanical abrasion is enhanced with this type of configuration, this type of configuration still cannot prevent chemical degradation of the photoreceptor surface by adjacent discharge.
Japanese Unexamined Patent Application Publication Nos. 2002-55580 and 2002-244487, for example, disclose image forming apparatuses that are provided with a device for applying a lubricant such as zinc stearate to the surface of the photoreceptor in order to both prevent an increase in the drive torque of a photoreceptor as a member being cleaned and to prevent toner or additives from fusing to the surface of the photoreceptor over long periods of time. This type of lubricant application is performed for the purpose of lowering the friction coefficient of the photoreceptor surface.
Japanese Unexamined Patent Application Publication Nos. 2002-244516 and 2002-156877, for example, propose application of a lubricant such as zinc stearate to the surface of the photoreceptor in order to solve the problem of notable occurrence of filming and fusing of toner on the photoreceptor surface in a case where the voltage applied to the charging member is a voltage in which an alternating current component is superposed on a direct current component.
Japanese Patent Application No. 2003-039538, for example, proposes an image forming apparatus in which zinc stearate is applied to the photoreceptor surface to protect it from degradation by the electrical discharge of the charging member.
The inventors (nine inventors) discovered that a necessary quantity of a protective substance must be interposed in the discharge area in order to prevent the film thickness reduction described above from occurring. Specifically, it was learned from the results of experimentation described hereinafter that degradation of the photoreceptor surface by electrical discharge is inhibited by the presence of a protective substance.
However, when such a protective substance is applied to the photoreceptor surface, the toner and the photoreceptor surface come into contact with each other at the developing part, whereby the inside of the developing device can become contaminated with the protective substance thus applied. Particularly when a large quantity of manuscript having a low image area ratio is output, since the majority of the toner on the development roller is returned with no change thereof to the inside of the developing device after coming into contact with the photoreceptor surface, the protective substance is scratched off by the toner and is entrained back into the developing device. When the inside of the developing device is contaminated with the protective substance, the characteristics of the developing agent are adversely affected, and it becomes impossible to maintain good image quality. When the amount of charge is reduced, for example, drawbacks occur whereby smudges, blocky lettering, and other types of image degradation occur, and a satisfactory image cannot be maintained over time. Furthermore, when the effects whereby the toner scrapes off the protective substance in this manner are severe, it also becomes necessary to increase the amount of protective substance to be supplied, which is not preferable in terms of device miniaturization. Therefore, a requirement exists for supplying this protective substance with better consistency and efficiency.